syslog-ng Premium Edition 7.0.20 - Administration Guide

Global and environmental variables

Starting with syslog-ng PE version 4 F1, it is possible to define global variables in the configuration file. Global variables are actually name-value pairs. When syslog-ng processes the configuration file during startup, it automatically replaces `name` with value. To define a global variable, use the following syntax:

@define name "value"

The value can be any string, but special characters must be escaped.To use the variable, insert the name of the variable enclosed between backticks (`, similarly to using variables in Linux or UNIX shells) anywhere in the configuration file. If backticks are meant literally, repeat the backticks to escape them. For example, ``not-substituted-value``.

The value of the global variable can be also specified using the following methods:

• Without any quotes, as long as the value does not contain any spaces or special characters. In other word, it contains only the following characters: a-zA-Z0-9_..

• Between apostrophes, in case the value does not contain apostrophes.

• Between double quotes, in which case special characters must be escaped using backslashes (\).

@define mypath "/opt/myapp/logs"
    source s_myapp_1 {
        file("`mypath`/access.log"
            follow-freq(1)
        );
    };
    source s_myapp_2 {
        file("`mypath`/error.log"
            follow-freq(1)
        );
    };
    source s_myapp_3 {
        file("`mypath`/debug.log"
            follow-freq(1)
        );
    };

@define mypath "/opt/myapp/logs"
    source s_myapp_1 {
        file("/opt/myapp/logs/access.log"
            follow-freq(1)
        );
    };
    source s_myapp_2 {
        file("/opt/myapp/logs/error.log"
            follow-freq(1)
        );
    };
    source s_myapp_3 {
        file("/opt/myapp/logs/debug.log"
            follow-freq(1)
        );
    };

Logging configuration changes

Every time syslog-ng is started, or its configuration is reloaded, it automatically logs the SHA-1 fingerprint of its configuration file using the internal() message source. That way any modification of the configuration of your syslog-ng clients is visible in the central logs. Note that the log message does not contain the exact change, nor can the configuration file be retrieved from the fingerprint. Only the fact of the configuration change can be detected.

The fingerprint can be examined with the logchksign command-line application, which detects that the fingerprint was indeed generated by a syslog-ng application. Just paste the hashes from the log message after the logchksign command like in the following example:

bin/logchksign "cfg-fingerprint='832ef664ff79df8afc66cd955c0c8aaa3c343f31', cfg-nonce-ndx='0', cfg-signature='785223cfa19ad52b855550be141b00306347b0a9'"

Modules in syslog-ng Premium Edition (syslog-ng PE)

To increase its flexibility and simplify the development of additional modules, the syslog-ng PE application is modular. The majority of syslog-ng PE's functionality is in separate modules. As a result, it is also possible to fine-tune the resource requirements of syslog-ng PE (for example, by loading only the modules that are actually used in the configuration, or simply omitting modules that are not used but require large amount of memory).

Each module contains one or more plugins that add some functionality to syslog-ng PE (for example, a destination or a source driver).

• To display the list of available modules, run the syslog-ng --version command.

• To display the description of the available modules, run the syslog-ng --module-registry command.

• To customize which modules syslog-ng PE automatically loads when syslog-ng PE starts, use the --default-modules command-line option of syslog-ng PE.

• To request loading a module from the syslog-ng PE configuration file, see Loading modules.

For details on the command-line parameters of syslog-ng PE mentioned in the previous list, see the syslog-ng PE man page at The syslog-ng manual page.

Loading modules

The syslog-ng Premium Edition application loads every available module during startup.

To load a module that is not loaded automatically, include the following statement in the syslog-ng PE configuration file:

@module <module-name>

Note the following points about the @module statement:

• The @module statement is a top-level statement, that is, it cannot be nested into any other statement. Usually it is used immediately after the @version statement.

• Every @module statement loads a single module: loading multiple modules requires a separate @module statement for every module.

• In the configuration file, the @module statement of a module must be earlier than the module is used.

@define autoload-compiled-modules 0